1. Field of the Invention
The present invention relates to a method and apparatus of controlling an image fixing temperature of an image forming unit in a laser beam printer, and particularly, to a method and apparatus of controlling an image forming unit of a laser beam printer and selecting one of a plurality of image fixing temperatures of the image forming unit depending on a period of time of a warm-up state and a ready state of the image fixing unit of the printer.
2. Description of the Related Art
An image forming unit in a copier, such as a laser beam printer or a plain paper facsimile machine, has been used for fixing a developer developed on a sheet of paper after heated to an image fixing temperature by a heater attached to the image forming unit. An image is formed by the developer on the paper using an electrophotographic developing method while the sheet containing the developer passes through the heated image forming unit. The heater of the image forming unit is controlled by a controller to maintain the image fixing temperature of the image forming unit for a next printing operating.
The image fixing temperature, however, is fixed to a certain temperature regardless of a period of time to warm-up the image forming unit and maintain a warm-up temperature until a printing operation starts. If the printing operation performs in a very short period of time after the temperature of the image fixing unit is increased to the warm-up temperature or the warm-up temperature is increased to a ready temperature, the quality of the printing operation is lowered because the image fixing unit is not fully but partially increased to the warm-up temperature or the ready temperature. The developer is partially fixed on the sheets of paper and the partially fixed developer becomes deteriorated because the temperature of the image fixing unit for fixing the developer on the sheet of paper is not uniformly maintained by repeated printing operations when the printing operation is performed shortly after the temperature of the image fixing unit is increased to the warm-up temperature or the warm-up temperature is increased to the ready temperature.
It is an object of the present invention to provide an apparatus and method able to prevent quality of an image fixed on a sheet of paper from deteriorating due to failure of maintaining of a proper image fixing temperature for each printing operation.
It is another object to provide an apparatus and method able to improve performance of an image fixing process in an image fixing unit of a printer.
It is yet another object to provide an apparatus and method able to provide a plurality of printing temperatures enabling an image fixing unit to properly fix a developer on each sheet of paper in each printing operation.
It is still another object to provide an apparatus and method able to select one of a plurality of temperatures in response to a period of time taken to maintain a ready temperature or a warm-up temperature for each printing operation.
It is a further object to provide an apparatus and method able to control a temperature of an image fixing unit in dependence upon a period of time between a printing start time and a warm-up start time or a ready start time in a printer.
It is also an object to provide an apparatus and method able to maintain an image fixing unit with a predetermined temperature suitable to fix a developer on consecutive sheets of paper.
These and other objects may be achieved by providing an apparatus and method of controlling an image fixing temperature in an image forming apparatus. The apparatus includes a controller storing a plurality of printing temperatures as the image fixing temperature, such as a normal temperature, a first temperature lower than the normal temperature, a second temperature higher than the normal temperature. The controller controls a heater attached to the image fixing unit with one optimum printing temperature out of the stored printing temperatures in dependence upon a period of time between a printing start time and a warm-up start time or a ready start time. The heater is turned on and off by the controller to maintain the optimum printing temperature. When a warm-up starts, the temperature of the image fixing unit is increased to a predetermined ready temperature. If a print command is not received until the warm-up is completed, the ready temperature is maintained. A printing operation starts upon completion of the warm-up even if the print command is received before the warm-up is completed.
In the method of controlling the image fixing temperature of the image fixing unit, when the printing command is received before the warm-up is completed, a normal temperature is set to the image fixing unit for fixing the image on a first sheet of paper, a first temperature is set to the image fixing unit for fixing the image on a second sheet of paper following the first sheet after a first sheet of paper is printed. The first temperature is higher than the normal temperature. If the print command is received while the ready temperature is maintained after the warm-up, a normal temperature is set to the image fixing unit for fixing the image on a sheet of paper. A second image fixing temperature is set to the image fixing unit for fixing the image on a sheet of paper if the print command is received in a predetermined period of time after the ready temperature is maintained after the warm-up. The second image fixing temperature is lower than the normal image fixing temperature.